1,721,037 research outputs found
Over 240 resonances on a metasurface-pixelated silicon wafer in an octave-spanning terahertz range
No full textMetasurfaces hold tremendous promise for various innovative sensing applications, thanks to their remarkable ability to manipulate light. A recent significant advancement in this research direction is using quasi-BIC (bound states in the continuum) metasurfaces for mid-infrared molecular sensing, which relies on creating a series of nearly uniformly spaced, sharp resonances on a single device. Although many studies have highlighted the potential of adopting this method in the terahertz (THz) regime, experimental demonstration is lacking. In this work, the first experimental demonstration of such frequency comb-like, quasi-BIC resonances on a single device is presented in the THz regime. By pixelating a 6-inch Si wafer with 25 different metasurfaces that possess both high-order quasi-BIC modes and a geometric scaling, a set of 241 sharp resonances ranging from 350 to 750 GHz is produced based on numerical simulation. By using a high-resolution vector network analyzer, 140 peaks that fall into the detection range from 500 to 750 GHz are confirmed experimentally, and their frequencies match well with the simulated results. By experimentally demonstrating frequency comb-like, quasi-BIC THz resonances on a single device, this work shows a new path for metasurface-based sensing in the THz regime.</p
Deep-subwavelength gap modes in all-dielectric metasurfaces for high-efficiency and large-angle wavefront bending
No full textAll-dielectric, phase-gradient metasurfaces manipulate light via a judiciously designed planar distribution of high and low refractive indices. In the established design approaches, the high-index elements play a dominant role, while the electromagnetic field existing between these elements is routinely viewed as either an incidental by-product or detrimental crosstalk. Here we propose an alternative approach that concentrates on exploring the low-index materials for wavefront shaping. In our Si metasurface, the low-index air gap between adjacent Si fins is judiciously tuned, while the high-index Si fins only have a single size across the whole metasurface. These gap modes provide the full 2π phase coverage, as well as high and relatively uniform transmission, at the deep-subwavelength scale. These characteristics are ideal for mapping a steep phase gradient, consequently suitable for high-efficiency and large-angle wavefront bending. This light manipulation capability is exemplified with numerical simulation in PW-SW (freely propagating wave to surface wave) conversion, where the wavefront is deflected by an angle of 90°. In the gap-mode meta-converters, the average unit size can be only 1/60 of free-space wavelength, an order of magnitude smaller than that of conventional all-dielectric metasurfaces. Their conversion efficiency can reach 68%, the highest value reported for any all-dielectric gradient metasurface THz converter
Provisioning Short-Term Traffic Fluctuations in Elastic Optical Networks
Get PDFTransient traffic spikes are becoming a crucial challenge for network operators from both user-experience and network-maintenance perspectives. Different from long-term traffic growth, the bursty nature of short-term traffic fluctuations makes it difficult to be provisioned effectively. Luckily, next-generation elastic optical networks (EONs) provide an economical way to deal with such short-term traffic fluctuations. In this paper, we go beyond conventional network reconfiguration approaches by proposing the novel lightpath-splitting scheme in EONs. In lightpath splitting, we introduce the concept of Split-Points to describe how lightpath splitting is performed. Lightpaths traversing multiple nodes in the optical layer can be split into shorter ones by SplitPoints to serve more traffic demands by raising signal modulation levels of lightpaths accordingly. We formulate the problem into a mathematical optimization model and linearize it into an integer linear program (ILP). We solve the optimization model on a small network instance and design scalable heuristic algorithms based on greedy and simulated annealing approaches. Numerical results show the tradeoff between throughput gain and negative impacts like traffic interruptions. Especially, by selecting SplitPoints wisely, operators can achieve almost twice as much throughput as conventional schemes without lightpath splitting
Directional conversion of a THz propagating wave into surface waves in deformable metagratings
No full textControllable conversion between propagating light waves and surface waves (SWs) has recently attracted significant research interests. This paper demonstrates, via numerical simulation, for the first time all-dielectric SW converters that possess a tunable and directional SW conversion efficiency. The SW converters contain multiple metagratings of Si pillars embedded in a deformable substrate. In the analysis, an infinitely large, bi-periodic metagrating under the illumination of linearly polarized light is considered first. The SW conversion efficiency of this metagrating can be modulated between 4.3% and 51.0% for incident light frequency at 0.8 THz by stretching the deformable substrate along the direction of SW propagation. Subsequently, two SW converters under circularly polarized light illumination are analyzed, where a similar level of efficiency modulation is retained in finite-sized metagratings. In these converters, only the metagrating channels along the stretch direction have a strong SW conversion efficiency, which can reach 40.4% after normalization against the effective grating area. The directivity, a parameter defined here to reveal the energy contrast among the output channels, reaches 38.6 in one of the converters. Due to its high tunability, high directivity and compact size, the SW converters may be used as tunable optical sensors and light couplers in the THz regime
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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